1. Field of the Invention
The present invention relates to methods and apparatus for the generation of gases. More particularly, the present invention relates to methods and apparatus for the generation of hydrogen and oxygen by the electrolytic dissociation of water.
2. Description of the Prior Art
It is well known that a gas, such as oxygen, hydrogen or chlorine, may be generated by disassociating a chemical compound into its constituent elements. The prior art describes several devices which utilize electrolytic cells for disassociating such compounds and generating gas. Such electrolytic cells take a variety of forms, but generally include a catalytic anode, a catalytic cathode and an adjacent electrolyte which is in electrical contact with both the anode and the cathode. A d-c voltage is applied across the catalytic electrodes to drive the reaction.
When reactants contact an electrode, they are dissociated into their constituent ionic forms, and the evolved gas is collected. For example, if water is placed in contact with the anode, an oxidation reaction will occur, disassociating the water to produce hydrogen and oxygen ions. The hydrogen ions move to the cathode where a reduction reaction produces hydrogen molecules, and at the anode the oxygen ions combine to form molecular oxygen. Generally, the electrolyte is a solid polymeric ion-exchange membrane.
Gas generators employing electrolytic cells may be used in many applications in place of compressed gas stored in cylinders. Moreover, electrolytic cells make possible the manufacture of inexpensive, compact devices for producing gas at the point of use. An example of an electrolytic cell gas generator is described in Dempsey et al. U.S. Pat. No. 3,870,616, which describes a hydrogen generator having a main water tank supplying water to the anode of an electrolytic cell for dissociation. However, not all the water supplied to the anode is dissociated. In fact, the bulk of the water supplied to the anode is transported with the dissociated hydrogen ions across the ion-exchange membrane into the cathode chamber. Part of this water returns to the anode chamber by diffusion back across the ion-exchange membrane; however, when gas is being actively generated, the rate of protonic pumping by the hydrogen ions is much greater than the diffusion rate of the water back across the membrane so that eventually a build up of water takes place in a accumulator chamber disposed above the cathode chamber. Whenever the water in the accumulator chamber rises above a predetermined level, a solenoid valve is closed to shut off the water supply from the main tank to the anode chamber. Nevertheless, as long as there is an electrical current supplied to the electrolytic cell, the dissociation reaction continues. In order to continue the reaction, and the production of gas, water must be supplied to the anode. However, the only water supplied to the anode chamber comes from the diffusion of water from the cathode chamber back across the ion-exchange membrane. During this period, the dissociation of the water is rate limited by the rate of water diffusing lack across the membrane.
"Drying out" or "breaking down" the membrane is a phenomenon which occurs when the electrolytic cell's demand for water is greater than the supply. The dissociation of water is driven by the current supplied to the electrolytic cell. As the current is increased, the quantity of water dissociated is increased. However, if the supply of water at the anode is not great enough to satisfy the demand of the electrolytic cell, the water molecules which were incorporated into the structure of the membrane during the manufacturing process will become dissociated. This irreversibly "dries out" the membrane, breaking down the polymer structure. As a result the output of the cell is progressively reduced, and the cell eventually becomes inoperable. This phenomenon will also occur if the generator accidentally runs dry, or loses its water through a leak in the system, or if the solenoid valve remains closed indefinitely.
The water contained in an electrolytic cell gas generator can become contaminated with impurities, such as metals, salts, acids, bases, or other electrolytes. Impurities such as these are contained in ordinary tap water. Once entered into the system, these impurities or contaminants are absorbed directly into the ion-exchange membrane, thereby "poisoning" the membrane and reducing the amount of uncontaminated surface area remaining to transport ions. As a result, the output of the cell is progressively reduced until the cell ceases to function entirely. This can be a gradual process or, if the amount of contamination is great enough, the membrane can be poisoned in a matter of minutes. Because these contaminants are invisible to an operator and electrolytic gas cell generators presently cannot detect if contaminated water is present, the ion-exchange membranes of these systems can be destroyed by the errant addition of tap water or other impure water into the generator.